Present methods of forming an implantation space between adjacent vertebral bodies in the human spine generally include the use of one or more of the following: hand held biting and grasping instruments known as rongeurs; curettes; drills and drill guides; rotating burrs driven by a motor; and osteotomes and chisels. Sometimes the vertebral end plate must be sacrificed as occurs when a drill is used to drill across the disc space and deeper into the vertebral bodies than the thickness of the bony end plate region. Such a surgical procedure necessarily results in the loss of the hardest and strongest bone tissue of the vertebral bodies located in the bony end plate region and thereby removes from the vertebral bodies that portion of its structure best suited to absorbing and supporting the loads placed on those vertebral bodies by an interbody spinal implant. Nevertheless, the surgeon must work upon the adjacent end plates of the adjacent vertebral bodies to access the underlying vascular bone that is capable of participating in the fusion by allowing active bone growth, and also to attempt to obtain an appropriately shaped surface in the vertebral bodies to receive the implant. Because the end plates of the adjacent vertebral bodies are not flat, but rather have a compound curved shape, and because the implants, whether made of bone or any other suitable implant material, when fabricated or manufactured, tend to have a geometric rather than a biologic shape, it is generally necessary to conform at least a portion of the vertebral bodies to the shape of the implant to be received therebetween.
It is important in forming the space between the adjacent bone structures to provide a surface contour that closely matches the contour of the implants so as to provide an adequate support surface across which the load transfer between the adjacent bone structures can be evenly applied. In instances where the surgeon has not been able to form the appropriately shaped space for receiving the implants, those implants may slip or be forcefully ejected from the space between the adjacent vertebral bodies, or lacking broad contact between the implant and the vertebral bodies, a failure to obtain fusion may occur.
Prior devices having a plurality of rotating cutting elements for removing bone with a drive mechanism between the cutting elements had limitations in certain applications. For example, if the bone to be cut was thicker than the individual thickness of each of the cutting elements, then the portion of the device between the cutting elements could hit the uncut bone and stop the bone removal device from advancing deeper into the bone being cut. Further, the presence of the drive member between the cutting elements kept the cutting elements spaced apart and thus could prevent the placement of the bone removal device into very narrow spaces such as, but not limited to, disc spaces as might be found in some instances in the cervical spine.
There remains therefore a need for an improved spinal interspace shaper that does not have such limitations so as to achieve the desired purposes as described herein.
The present invention relates to a bone removal device for insertion into and at least in part across the height of a disc space between adjacent vertebral bodies in the human spine, and a guard for providing protected access to the disc space and for maintaining a desired positioning of the adjacent vertebral bodies relative to each other, and to a method of working on those portions of the vertebral bodies adjacent that disc space to remove bone material sufficient to form a desired contoured end plate and to thereby access the underlying vascular bone. For purposes of this application, the bony xe2x80x9cend plate regionxe2x80x9d of the vertebral bodies is defined as the outer shell of compact bone (the bony end plate) adjacent to the spinal disc and the underlying subchondral zone.
The apparatus and associated method of the present invention is adapted to form a surface on or into each of the vertebral body surfaces that are adjacent the intervertebral disc space. The prepared spaces are formed through the inert outer bone of the vertebral bodies to get to the vascularized underlying bone, preferably, without generally removing all of the thickness of the end plate region. The formed surface(s) have a defined shape and a contour corresponding to a preferred interbody spinal implant to be implanted in the disc space.
The bone removal device of the present invention is useful in the cervical, thoracic, and lumbar spine from anterior to the transverse processes of the vertebrae, lateral or anterolateral in the thoracic and lumbar spines, or from posterior in the lumbar spine. The bone removal device, in a preferred embodiment, generally includes a cutting element movably and preferably replaceably mounted on the distal end of a shaft. A depth limiting mechanism preferably controls the depth of insertion of the cutting element into the intervertebral space (i.e., the disc space). The device also includes a handle that may be detachable from the shaft. As used herein, the term xe2x80x9chandlexe2x80x9d refers to a portion of the device that a surgeon may grip or otherwise manipulate to guide the working end of the device. That xe2x80x9chandlexe2x80x9d may in fact have multiple purposes. For example, the handle may be a portion of the shaft on which the working end is mounted at one end. Alternatively, the handle may be part of a segment that connects the device to a power source. For example, the handle may be part of a power source that supplies pressurized gas to the power source if turbine driven, or the handle may be a drill, but the term xe2x80x9chandlexe2x80x9d is used herein in its broadest context to refer to that which the surgeon grasps to use the present invention.
Additionally, the shaft may be detachable from the working end. The device also includes a drive mechanism that transmits power to activate, i.e., move, the cutters. The drive mechanism connects to an energy source, e.g., a rechargeable battery that further may be but need not be housed within the handle of the device. By way of example only, the drive mechanism may include an electric motor or an electromagnetic oscillating mechanism. Or, again by way of example only, the drive mechanism and handle in which it may be disposed may include the head unit of a gas powered turbine of a type commonly used in other surgical instruments.
In a preferred embodiment, the working end is generally as wide as the spinal implant to be implanted or the width of a combined plurality of implants adapted for side-by-side use between the adjacent vertebral bodies adjacent the disc space. The receiving bed, i.e., the prepared surface of the vertebral bodies, when formed by the device, will correspond in shape, size, and contour to the corresponding surfaces of a preferred spinal implant or combined width of implants to be implanted. The surface produced by the bone removal device is generally flat or concave to correspond to the upper or lower vertebral body contacting surfaces of the implant that will be implanted between the vertebral bodies. In an embodiment of the present invention having domed or convex upper and lower cutters or cutting members the device may be inserted into the spine and then turned on to form to desired shape into the adjacent vertebral bodies. The cutters have a leading end that is capable of cutting through bone and/or disc material to form a pocket or socket having a contour corresponding to the forward aspect of the leading end, as well as at least a portion of the side surfaces of the preferred implant to be implanted. These sidewalls assist in restraining the implant from lateral movement.
The working end of the present invention includes a pair of opposed, outwardly facing cutters which lie in planes that may be either parallel to each other or, alternatively, convergent to each other. The present invention saves time by simultaneously preparing both of the vertebral end plates adjacent a disc space. The bone removal device shapes the three-dimensional space created between the adjacent vertebral bodies, which space can be made to conform to the desired lordosis of that portion of the spine that will receive the implant. The end plate space may be, but need not be, identical to the height of the implant, as the implant may be there to optimize the distance of the disc space.
The drive mechanism of the bone removal device is preferably located adjacent the working end of the instrument permitting a reduction in the overall height of the cutting elements. This configuration permits the overall height of the cuffing mechanism to be thicker or given the same height, it can be less than what was previously possible with the cutting elements having a drive member therebetween because the cutting elements can be placed closer together. A reduced overall height of the cutting mechanism permits the placement of the bone removal device into narrower spaces, such as but not limited to disc spaces as might be found in some instances in the cervical spine, than previously possible. Moreover, because the space between the cuffing elements is minimized, the thickness of the cuffing elements may be increased.
The cutting element of the present invention is not limited to being a unitary, one-piece construction, regardless of the number of cutting surfaces of the cutting element. The cutting element may include multiple pieces that, by way of example and not limitation, are mountable on the end of the device to, in combination, define the overall shape of the cutting element and its surfaces. Thus, the term xe2x80x9ccutting elementxe2x80x9d is used herein to refer to both a unitary, one-piece construction or a multi-piece construction.
The cutting element is preferably mounted on the mounting member and may be removable and interchangeable. In such an embodiment, the mounting member may be, but does not have to be, attachable to a shaft that is attachable to the handle. The cutting element and the mounting member may be separable from each other. Alternatively, the working end and the mounting member may, together, be removable from the handle.
While a preferred embodiment of the present invention is discussed and disclosed herein for creating a space between adjacent vertebral bodies in the spine, the present invention is not limited to a device for creating a space between adjacent vertebral bodies, but can also be used in other portions of the body where it is desirable to place an implant between adjacent bone structures. Furthermore, an embodiment of the present invention may have upper and lower cutting surfaces that are in angular relationship to each other so as to, for example, match the natural lordotic curvature of the human spine at the location of the vertebral bodies to be operated upon. Additionally, sequentially larger, that is wider and/or thicker, ones of the cutting elements, or mounting member, may be used to form the desired sized space in a step-wise fashion, or the working end may be sized to substantially match the final desired width of the surface to be formed in the vertebral end plate. Furthermore, the working end is preferably configured with a sharpened leading edge to allow the working end to xe2x80x9cforward cutxe2x80x9d as it is inserted between the adjacent vertebral bodies. In this manner, progressive insertion of the cutting element between the vertebral bodies is facilitated.
In a preferred embodiment, a guard for use with the bone removal device has a body with a passageway passing therethrough. In a preferred embodiment, a first disc penetrating extension and a second disc penetrating extension extend from the leading end of the guard and are adapted to be inserted into the disc space between adjacent vertebral bodies. The disc penetrating extensions are preferably adapted to distract and align the disc space, and restore lordosis. The disc penetrating extensions also further limit lateral excursion of the bone removal device and protect vital structures lateral to the disc space. In the alternative, the guard could be attached with screws or pins to each of the vertebral bodies like portions to bear upon the end plates.
The guard provides protected access to the disc space and the adjacent vertebral bodies for the working end of the bone removal device through a passageway, which may be sufficiently taller than the height of the space to be formed by the working end so as to allow for the sequential use of working ends of increasing height or the insertion of a spinal implant taller than the height of the working end thereby allowing the surgeon the option of keeping the guard in place after the cutting procedure. For example, the guard can be left in place distracting and aligning the adjacent vertebral bodies after the cutting step so that spacers (i.e. trial implants) can be trialed and then the implant of the optimal height, and perhaps of a greater height than the cutter, can be inserted.
The bone removal device preferably remains appropriately positioned relative to the height of the passageway during the cut. By way of example and not limitation, this may be achieved by having the bone removal device and guard aligned by a cooperative track, or a longitudinal groove and cooperating protrusion. In an alternative embodiment, a mounting element may be located between the cutting portion at the leading end of the bone removal device and the trailing end of the bone removal device. In a preferred embodiment, the mounting element can be taller than the cutting portion. When the taller mounting element passes through the passageway of the guard, it contacts the interior of the passageway to maintain the cutting portion in a preferred orientation to the guard so that the cutting portion can form an implantation space of a height less than the height of the passageway that is still properly positioned relative to removing the dense thickness of bone from each of the vertebral bodies adjacent the disc space being prepared. This height differential permits an implant having a height greater than the height of the implantation space to be inserted through the guard. Somewhere along the shaft an enlarged portion may cooperate with the inner height and even the rearward portion of a guard.
The leading end of the guard may have a foot plate adapted to contact the vertebral bodies when for use generally anteriorly or anteriorlaterally and may be contoured to generally conform to at least a portion of the exterior aspect of the vertebral bodies where contacted. The foot plate may have holes for receiving, for example, fasteners including spikes, bone screws, pins, prongs, nails, or the equivalent therethrough to secure the foot plate to the vertebral bodies or such spikes, bone screws, pins, prongs, or nails maybe part of the foot plate. The attachment of the guard with fasteners to the adjacent vertebral bodies may further secure the vertebral bodies in the desired relationship and hold the vertebral bodies steady for the cutting operation to be performed.
For use posteriorly, it is generally preferred that the guard have at least one and more preferably two disc penetrating extensions, such that a foot plate may be minimized or absent.
Thus, the present invention provides a device and method for preparing a disc space between adjacent vertebral bodies to receive a spinal implant, and prepares that disc space by removing a portion of the bony end plate region of those vertebrae adjacent that disc space to form predetermined surfaces in that vertebral bodies adjacent the disc space. The prepared spaces are formed through the inert outer bone of the vertebral bodies to get to the vascularized underlying bone, preferably, generally without removing the full thickness of bone in the end plate region. The prepared surfaces are sized and contoured to have broad intimate contact with the preferred spinal implant to be implanted between the adjacent vertebral bodies and along side walls of a socket, which broad contact provides for increased implant stability. This broad area of intimate contact between the vertebral bodies and the implant promotes bone ingrowth from the vertebral bodies into the implant, and also provides a broad area over which to support the incumbent loads so as to minimize the risk of vertebral collapse or subsidence of the implant into the vertebra.
While the present invention has been generally described above, and the preferred embodiments of that invention will be described in detail below, neither that general description nor the detailed description limits the scope of the present invention. That scope is defined by the claims appearing at the end of this patent specification.
It is an object of certain embodiments of the present invention to provide a device and method for quickly, safely, effectively, and accurately working upon the region of the bony vertebral body end plate regions adjacent a disc space so as to, while preferably preserving bone of that region, to at least in part, remove bone such that to access the active bone growth end plate at least in part, remove bone to produce a socket to accept and implant corresponding in size, shape, and contour to an implant to be implanted between the adjacent vertebral bodies.
It is a further object of certain embodiments of the present invention, to provide a device capable of simultaneously working upon both of the vertebral body end plate regions adjacent a disc space to produce opposed receiving surfaces in the adjacent end plate regions corresponding in size, shape and contour to a preferred implant to be implanted, and in so doing to define the shape of the implant space.
It is a further object of certain embodiments of the present invention to provide a vertebral interspace preparation device that, in a preferred embodiment, is capable of working with linear insertion, i.e., insertion along a single axis, and without the need to substantially move the device from side to side within the disc space along a second axis. In such a preferred embodiment, the device has at a working end having a width generally corresponding to the width of the implant to be implanted, and a leading edge corresponding to a generally arcuate leading end of the implant to be implanted, for creating a space of a fixed geometry corresponding to an implant of corresponding dimensions.
It is a further object of certain embodiments of the present invention to have a safety mechanism built into the device that limits the depth of insertion of the device into the spine.
It is a further object of certain embodiments of the present invention to provide a vertebral interspace preparation device that can have interchangeable working ends so as to be capable of producing a variety of differently sized and contoured surfaces and shapes within the intervertebral space.
It is a further object of certain embodiments of the present invention to have cutters extending to the leading end of the device such that the device may remove bone along its leading end as it is advanced within the disc space.
These and other objectives of the present invention will occur to those of ordinary skill in the art based on the description of the preferred embodiments of the present invention described below. However, not all embodiments of the inventive features of the present invention need achieve all the objectives identified above, and the invention in its broadest aspects is not limited to the preferred embodiments described herein.